Traditionally, a mortar system was an infantry and commando weapon that was designed for man-packing. It had to be broken down into a few sub-assemblies to resolve the weight constraint necessitated by man-packing. Therefore, to set up the mortar system for firing will take at least a few minutes. However, mortar systems have now been mounted on various vehicles to meet the quick response required in performing hit-and-run missions demanded in modern warfare.
The traditional mortar system consists of a barrel and breech assembly, bipod assembly and a base-plate. The breech piece has a spherical joint with the base-plate sitting on the ground. The bipod assembly is used for supporting the barrel and for fine adjustment of its elevation and travel. The gas pressure acting on the breech and the reaction force generated during firing, which are subsequently transmitted onto the structure (base-plate) is very high. It could be as high as 150,000 kPa, but it is not a problem for a solid structure such as a base-plate that sits on the ground and acts as a natural damper.
When the mortar system is platform-mounted (in particular when it is mounted on a vehicle), most system integrators currently use the traditional mortar system and focus on designing the structure to withstand the firing force. This will result in heavy structural reinforcement/modification of the mounting platform (vehicle). The damping adapter has been developed by some system integrators as an interface between the mortar and the platform (vehicle) which is able to reduce the firing force to about 40%. However, even with a 60% reduction (60,000 kPa) of the firing force, it is still very large and requires a heavy structure to withstand it. The suspension system also requires reinforcement if the platform (vehicle) is designed to fire on it.
The following problems have been borne in mind when solving the deficiencies, such as lack of recoil buffering and accuracy of the mortar systems of the prior art, and the lack of manoeuverability of the whole vehicle.
Recoil Mechanism
The recoil buffer mechanism is the most essential part of the gun system. The traditional mortar system is designed for man-packing and therefore its weight must be relatively lighter to allow portability. Thus the recoil mechanism has never been considered for use in the mortar system. However, when the mortar system is platform-mounted (vehicle-mounted), the recoil forces become more critical compared to the weight of the individual sub-assembly. Hence, some system integrators have incorporated the recoil mechanism to absorb the high recoil force, but this mechanism may not be efficient as the recoiling mass is too low to absorb the firing energy effectively and subsequently convert it to the recoil braking force.
Cradle Design of Conventional Gun Systems
“O”-cradle designs, “U”-cradle designs and a combination of both are the three most common cradle designs in gun systems that are used for the support and guidance of the recoiling mass during firing.
The “O” cradle design is the first-generation gun cradle design. It has two bushes at both ends of the cradle to support and allow the barrel to slide on its outer cylindrical surface when recoiling during firing. It is the simplest in construction and the most commonly-used design. The big and long cylindrical sliding surface on the barrel carries an excessive amount of weight. On the other hand, there are minimum number of parts attached on the recoiling mass, which reduces the effectiveness of the buffering of the recoil.
The “U” cradle design is the second-generation gun cradle design. The “T” shaped slot on the cradle is used to support and guide the barrel while recoiling during firing. Two brackets are attached onto the barrel (or one on the barrel and one on the breech) as a bridge between the barrel and cradle. The external profile of the barrel can be optimized to achieve the design strength (gas pressure distance profile). Hence, there will be significant weight reduction on the barrel. The recoil cylinder can be attached together with the barrel to increase the recoiling mass to reduce the recoiling force. However, the cradle is complex in both design and manufacturing.
The “O” and “U” combination cradle design takes advantage of the benefits of both the above designs. Its front support is an “O” cradle design and its rear side is a “T” cradle design. The cylindrical surface of the barrel on its centre portion is used for front sliding and only one bracket is attached onto either the barrel or on the breech as the rear support. The barrel external profile is very close to an optimized design and it saves one bracket. The cradle is, however, complex in both design and manufacturing. Regardless of all the three types of cradle design, the minimum length of the cradle will be two×support length+recoiling length+safety allowance.
Muzzle Brake
To-date, the muzzle brake has not been adopted onto any mortar system. The traditional mortar system is designed to be man-packed. Its weight is very critical. Therefore, the muzzle brake has never been considered for the mortar system.
The bomb muzzle velocity is very much slower than the gas flow when it leaves the barrel. The bomb will be unstable because of gas turbulence at the muzzle. Trying to re-stabilize the flight path of the bomb during flight will result in the bomb losing its kinetic energy and accuracy.
Elevating and Traversing Mechanism
The most common elevating mechanisms used in gun design are the arc and pinion gear design, the single actuator at the centre, or two actuators installed on both sides of the elevating mass in parallel. The base width of these mechanisms is quite small.
The arc and pinion gear or linear actuator are most commonly used for the traversing mechanism. In the arc and pinion mechanism, backlash (clearances) in the gear trains is essential to ensure the smooth running of the mechanism. The acceptable backlash in the traversing mechanism for accurate gun laying demand high precision and costly components. Alternatively, complex anti-backlash mechanisms are normally employed to resolve the problem. Another disadvantage is that the gear teeth have friction due to their relative movements and are prone to wear and tear since it is very difficult to protect against dust and dirt in its operating environment. The uneven wear and tear will cause malfunction of the anti-backlash mechanism after prolonged usage.
The linear actuator is only used in traverse mechanisms having a smaller arc of traverse. Furthermore, it has a non-linear (cosine error) correlation movement between the linear actuator and the rotating action. This will complicate the control system for a closed-loop power drive system.
The invention herein seeks to overcome most of the disadvantages in the prior art mentioned above.